Ferns are dying in Kitsap forests, and nobody knows why

Camp Indianola director Darin Gemmer, top, and John O'Leary, water resource program manager for the Suquamish Tribe, stand near a spot of dead ferns on a trail. Plant experts are trying to understand why sword ferns are dying off in North Kitsap and other parts of Puget Sound.(Photo: Larry Steagall / Kitsap Sun)Buy Photo

INDIANOLA — The barren patch of ground stood out in the midst of the lush forest understory.

All around, sword ferns crowded between tree trunks forming dense thickets of greenery, but in this spot, the ferns had been decimated. Slender dead leaves littered the ground and only bare stubs remained where clumps of healthy fronds recently flourished.

"As far as I can recall, this was our ground zero," Camp Indianola director Darin Gemmer said, pausing on a hike along one of the camp's trails on Thursday.

The barren spot was one of many fern die-off sites Gemmer and John O'Leary, a water resources program manager for the Suquamish Tribe, stopped to point out along the path. Over the past year, Gemmer, O'Leary and others have watched with alarm as large patches of sword fern — a ubiquitous plant in the Northwest — disappeared in North Kitsap forests.

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Camp Indianola Director Darin Gemmer puts up a sign closing a camp trail. He and others are working to understand what could be killing off sword ferns on the property.(Photo: Larry Steagall / Kitsap Sun)

The mysterious die-offs have been documented in other places around Puget Sound, but nobody knows for sure what's killing the ferns. An alliance of scientists, park stewards, students and amateur naturalists have worked for years to find a cause but so far come up empty.

Some, like O'Leary, worry that whatever is destroying sword ferns could be hurting other native species.

"That it's unknown and it may be affecting habitat in ways we don't understand, that frightens me," he said.

It's worrisome to Tim Billo, a University of Washington biologist who's enlisted students to monitor sword fern die-off at Seattle's Seward Park, where the phenomenon gained widespread attention.

"We've narrowed down a lot of things that it isn't, but we haven't identified the cause, which is disturbing and alarming," Billo said. "Every year it seems to get bigger."

A mysterious killer

Naturalist Catherine Alexander first raised the alarm about a sword fern die-off in Seward Park in 2013. The ferns — many likely hundreds of years old — dominate the understory of the 120-acre park. But over the past few years, large swaths have turned brown, died back and not regrown.

Experts believe changes in climate and weather patterns are unlikely to be causing the phenomenon. The die-offs have been reported in wet and dry years. If changes in climate were killing the species, the damage would be more uniform across the region. Instead, the die-offs begin in concentrated pockets and the destruction radiates outward, as though an epidemic is spreading.

Other theories, like the colonization of invasive earth worms, have been floated but not substantiated. After years of investigation, the source of the die-offs remains frustratingly elusive.

"What we're seeing is not symptomatic of any known pathogen," Billo said.

The fact that sword ferns are typically tough to kill makes their disappearance all the more strange.

Gardeners and hikers may find ferns pleasant but they don't capture the imagination as readily as a majestic eagle or towering cedar. Sword ferns have virtually no economic value, Barrington added.

Instead, the plants offer a more subtle benefit to the surrounding forest, contributing to biodiversity, providing habitat for woodland animals and colonizing open areas that might otherwise be overrun over by invasive species.

"The sword fern is a key ecological contributor to its community," Barrington said.

To Bloedel Reserve plant expert Darren Strenge, sword ferns are an integral part of the Northwest landscape.

"I consider it iconic and representative of Western Washington forests, and it's disappearance would drastically change the character of our forests," Strenge said. "It would be like a part of our natural identity died."

O'Leary with the Suquamish Tribe admits he didn't think much about ferns in the past.

"I remember walking through the woods and being annoyed by how many ferns there were," he said.

Now the mystery of their disappearance has become a near-obsession for the water resources specialist. He carries a GPS unit to plot die-off areas and follows game trails through the forest to uncover more dying patches. At an affected property in Suquamish, O'Leary erected raised garden beds and planted ferns in clean soil and in soil from a contaminated site to test whether the pathogen was present in the dirt.

Back at Camp Indianola on Thursday, Gemmer pounded in bright red signs warning walkers the trails were being closed to quarantine the unidentified fern disease.

"We haven't used the trails this summer just so we're not spreading it around," Gemmer said.